1. Field of the Invention
The present invention relates to a curable composition favorably used in ink compositions, paints, adhesives, and the like, an ink composition containing the curable composition favorably used in inkjet recording, an inkjet recording method, a printed material prepared by using the inkjet recording method, a planographic printing plate obtained by using the ink composition, and a method of producing a planographic printing plate.
2. Description of the Related Art
Cyclic ether compounds for example of 3 -or 4-membered ring are known to exhibit high reactivity, and have been used as a polymerizable compound to be contained in curable (compositions to which thermal polymerization such as that using photocationic polymerization or acid anhydride is applied (see, for example, Japanese Unexamined Patent Publication (JP-A) Nos. 11-43540 and 11-60702).
In addition, active energy ray curing inkjet inks containing an epoxy compound having its oxirane rings connected to each other via a connecting chain having a branched structure have been proposed. However, the connecting chain in the epoxy compound, which is a hydrophobic connecting chain, caused a problem that the ink therefrom is lower in adhesiveness to the recording medium (see, for example, JP-A No. 2005-41892).
There are many image-recording methods of forming an image on a recording medium such as paper based on image data signals, including those in electrophotographic process, sublimation or fusion heat-transfer process, and inkjet process. Among them, the inkjet process is advantageous in that it allow printing in a cheaper device at a lower running cost, because it forms an image directly on a recording medium by ejecting ink only in desirable image region and thus uses the ink more efficiently. In addition, the inkjet process is also less noisy and thus advantageous as an image-recording method.
The inkjet process allows printing not only on plain paper but also on non-water-absorptive recording media such as plastic sheet and metal plate, but recently, there is an urgent need for acceleration of printing and improvement in image quality in the process. The period needed for drying and curing the ink droplet after ejection has a great influence on the printing efficiency and the quality of printed image.
In the inkjet recoding processes, there is a recording method by using an inkjet recording ink that cures by irradiation with radiation ray. In the method, it is possible to improve the printing efficiency and the quality of image, by curing the ink droplet by irradiating it with radiation ray immediately or after a particular period from ejection.
If it is possible to raise the sensitivity of such an inkjet recording ink that cures by irradiation with radiation ray such as ultraviolet light or to raise the efficiency of the ink curing by radiation ray, it is possible to obtain many benefits, such as improvement in inkjet recording efficiency, reduction of power consumption, elongation of the lifetime of radiation ray generator due to decrease in the load, and prevention of evaporation of low-molecular mass substances due to insufficient curing. In addition, the improvement in sensitivity is effective in increasing the strength of the image formed with inkjet recording ink, and in particular, when the ink composition is applied to preparation of planographic printing plates, it leads to increase in the hardness of the image part and thus to increase in printing durability.
Such an inkjet process by using an ink composition that cures by radiation ray such as ultraviolet light is attracting attention recently, as the ink composition is relatively odorless and fast-drying, and allows recording on a recording medium that absorbs a smaller amount of ink; and ultraviolet light-curing ink compositions that harden in radical polymerization for use in the inkjet process are disclosed (e.g., Japanese Patent Application Laid-Open (JP-A) Nos. 63-235382, 3-216379, and 5-214280, and Japanese Patent Application Publication (JP-B) Nos. 6-21256 and 6-62905).
In addition, for the purpose of providing an inkjet recording ink that gives an image higher in sensitive and adhesiveness to the recording medium without ink bleeding, even when printed on a support, on which it is normally difficult to record by the inkjet recording method, and that is higher in stability without smaller skin irritation or sensitization, compositions containing polymerizable compounds of particular radically polymerizable acrylates and a colorant were disclosed (e.g., JP-A Nos. 2003-192943 and 2003-192944).
These radically polymerizable inks are superior in curing speed and give an image without ink bleeding, but also had a disadvantage that the adhesiveness to recording medium deteriorates by the volume shrinkage during curing.
Accordingly, for the purpose of improving the adhesiveness to recording medium, cationically polymerizable ink compositions resistant to the shrinkage during ultraviolet light-curing were proposed (e.g., JP-A No. 9-183928). However, these cationically polymerizable inks had an insufficient stability during storage because of the reactions of the acids generated therein over time, which was the great obstacle for commercialization of these inks. For improvement in the storage stability, methods of adding a basic compound or a thermal base-generating agent were proposed (e.g., JP-A Nos. 2003-312121, 2003-341217 and 2004-91558). However, use of a basic compound resulted in emergence of a new problem that the curing efficiency of ink was lowered by the basic compound added, because it inhibited the function of the acid generated by light exposure.
In addition, conventional curable compositions such as the inks described above caused a problem of undesirable progress of curing reaction when stored under a high-temperature environment.
Currently as described above, there is still no curable composition that can be applied to UV curing ink composition, form a film highly sensitive to radiation ray irradiation and superior in strength and is also heat resistant.